Metalness and PBR work flow Film and TV

[johnnelsonvfx]

Question - Currently we are trying to rework our asset\texturing pipeline at our studio. We have a new asset supervisor that is trying to convince us to be a completely pbr workflow for Film\TV studio. This is great and all but we render a lot of coated material things like Cars,Planes etc. My question is two part,

1. Can you have a metalness pbr work flow that utilizes blend materials for coated materials like cars.
2. If no, then does PBR workflow take away the blend material work flow or make it "wrong"?

[Morbid Angel]

1 - if I understand correctly you wish to blend two vray materials there is no reason that metalness would not work. You blend materials by a mask, each material has its own metalness, so then it should be just fine. Since for car paint vray carpaint does not have metalness or glossy frenel for that matter, its not possible to use it in a pbr scenario. However that said, pbr is just a way of working, a consistent way that is, where if you use the output from substance for example in each dcc package it will be the same if all maps are plugged in and rebuilt shader correctly.

[dgruwier]

Just to be clear, I assume we're talking about using a PBR texturing workflow in which you have a metalness map and a combination diffuse and reflection color map, piped into a single material.

Technically there shouldn't be any problems with coatings and such. The biggest downside is that transition areas between metals and regular materials are going to be incorrect. For example if you have a PBR material that consists of metal covered with soft layers of dust, you'll have a weird, impossible material in the middle of the transitions, something like a half-metal that is half-dust colored. You'll also be blending your glossiness values which will cause all kinds of problems.

If you want a practical demonstration you can do it like this:
Use a gradient ramp to blend between a metallic and a dust material using a VRayBlendMtl. Then try using the the same ramp to blend between the diffuse, glossiness and IOR values you picked for each material, and pipe them into a single material with the ramp as the metalness map, to mimic a PBR workflow. Render the two setups side by side on a sphere with HDR lighting. I'd send a scene file or screenshot as an example, but our network prohibits uploading files.

We always try to keep materials as separated as possible, having one material for dust, one for limescale, one for metal, one for rust, etc, with masks to blend between each. But even if you don't go with that extreme, I'd still suggest trying to find a way to not have the metal materials share their diffuse and glossiness maps with other materials.

So yeah, unless you're doing realtime rendering in a game engine, I would not recommend a full PBR workflow. You're going to make some sacrifices to the physical accuracy that are accepted in games for the performance improvement it gives, but are pointless for offline rendering IMO where you can easily afford to wait those few seconds per frame.

[Vizioen]

I'd send a scene file or screenshot as an example, but our network prohibits uploading files.

Offoptic: How do you send emails/files to clients? Or do anything else for that matter, isn't uploading part of surfing the web

Ontopic: AFAIK it's possible to have materials blend (with vertexpainting or so) in Unreal and similar, so keeping materials separate and working full PBR is still an option or am I missing something?

[dgruwier]

Offoptic: How do you send emails/files to clients? Or do anything else for that matter, isn't uploading part of surfing the web

Producers have upload access through a restricted and firewalled FTP setup, and artists have internet browser access through a virtual machine on a server that we remote into (which doesn't allow file transfer).

Ontopic: AFAIK it's possible to have materials blend (with vertexpainting or so) in Unreal and similar, so keeping materials separate and working full PBR is still an option or am I missing something?

That's why I clarified that what I understood johnnelsonvfx to mean by "PBR" asset workflow is to have one material, with one set of texture maps including a metalness map, like this.

If that's not the case, then I can't think of any downsides, because aside from the metalness and single material workflow thing, the rest of what game artists call PBR were already part of correct offline rendering (energy conversation, glossiness maps, not baking AO into diffuse, etc.), which are all good things.

[^Lele^]

energy conversation

Besides agreeing with you thoroughly, this typo had me in tears, for some reason.
I started seeing hippies handy-waving the universe's energies to one another...

[Vizioen]

[dgruwier]

Haha yeah it sounds like something the New-Age Bullshit Generator might come up with

Also, back on topic I found an excellent image demonstrating the transition area problem I mentioned with a one-material PBR workflow. This is a comparison between using just a specular map vs metalness + glossiness, but the edge artifacts are also solved by using layered materials instead of forcing everything into one map.

[^Lele^]

Behind the tears of laughter, i don't seem to be able to see the image you posted.
Should I stop "reionizing electrons", or is it an issue on your side?

[Vizioen]

After a google search I've found this:

[Ihno]

I once got around those artifacts by using a blend mtl and use the metalness tex as blend amount for a metal material.
I'f only the render could look like that rightaway.. Is this something that could be fixed?

[dgruwier]

It's not a software limitation, it's an inherent limitation of the workflow. It's fixed by doing exactly what you did.

Also, thanks Vizioen that was it

[Ihno]

Yea, I know.. But who knows...
Chaos group might be able to change the way the grayscale values are rendered to something that looks more like using a blend mtl.

[Morbid Angel]

After a google search I've found this:

This is an issue with a use of normal map I believe from substance. I'm not sure how this is setup of course, but I'v encountered this several times and it was related to normal map.

[dgruwier]

This is an issue with a use of normal map I believe from substance. I'm not sure how this is setup of course, but I'v encountered this several times and it was related to normal map.

It is from this article about PBR texture conversion, and I posted it specifically because it depicts the problem with transition areas I was describing. From the article:

However, one of the drawbacks to storing both diffuse and specular content in the same texture is artifacts along material transitions.

You have an area of the texture map where the metalness texture is at 1, and the diffuse color is white (for the metal), and you have an area of the texture map where metalness is 0, and diffuse color is dark gray (for the dark paint). These two individual materials are correctly defined.
In between, you have pixels where metalness is 0.5, and the diffuse color is light gray. That gives you an impossible material that is a mix of dark metal + bright paint, which causes the artifact.


Ihno's If you want one pixel defined by multiple glossiness/diffuse values, you need multiple shaders. That's all there is to it.